This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A138723 #3 Mar 30 2012 17:33:54 %S A138723 1,3,11,19,37,4,12,20,38,21,39,22,40,23,41,24,42,25,43,26,44,27,45,28, %T A138723 46,29,47,30,48,5,13,31,49,6,14,32,50,7,15,33,51,8,16,34,52,9,17,35, %U A138723 53,2,10,18,36,54 %N A138723 Atomic numbers of the periodic table of the elements, read downwards along 18 columns, up to the 5th period. %C A138723 This finite sequence has 54 members. Atomic numbers > 54 are not members. %e A138723 =========================================================== %e A138723 ........... THE PERIODIC TABLE OF THE ELEMENTS ............ %e A138723 =========================================================== %e A138723 P/G: 1A 2A 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B 3A 4A 5A 6A 7A 8A %e A138723 =========================================================== %e A138723 (1): .1 .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .2 %e A138723 (2): .3 .4 .. .. .. .. .. .. .. .. .. .. .5 .6 .7 .8 .9 10 %e A138723 (3): 11 12 .. .. .. .. .. .. .. .. .. .. 13 14 15 16 17 18 %e A138723 (4): 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 %e A138723 (5): 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 %e A138723 =========================================================== %Y A138723 Cf. A099955, A134984, A138724, A138725, A138726, A138727. %K A138723 easy,fini,full,nonn,tabf %O A138723 1,2 %A A138723 _Omar E. Pol_, Mar 26 2008, Jan 25 2009